Transition frequency multiplier semiconductor device

ABSTRACT

A transition frequency multiplier semiconductor device having a first source region, a second source region, and a common drain region is disclosed. A first channel region is located between the first source region and the common drain region, and a second channel region is located between the second source region and the common drain region. A first gate region is located within the first channel region to control current flow between the first source region and the common drain region, while a second gate region is located within the second channel region to control current flow between the second source region and the common drain region. An inactive channel region is located between the first channel region and the second channel region such that the first channel region is electrically isolated from the second channel region.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/014,348, filed Feb. 3, 2016, which claims the benefit of U.S. provisional patent application No. 62/111,869, filed Feb. 4, 2015, the disclosures of which are incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure is related to semiconductor devices that are configured to extend transition frequencies for millimeter wave (mmW) and beyond radio frequency applications.

BACKGROUND

Often a semiconductor technology's usefulness for the radio frequency (RF) space can be characterized by the transition frequency (fT)-breakdown voltage product known as the Johnson-limit. A high fT-breakdown product can be obtained by using semiconductor technologies that possess high electron velocity and wide energy band-gap. A gallium nitride (GaN) high electron mobility transistor (HEMT) is an example of a semiconductor device that possesses high electron velocity and a wide energy band-gap.

In addition, multi-transistor circuit topologies such as the Darlington-pair, cascode, and multi-stacked transistors can be used to improve the fT-breakdown product through higher voltage operation, fT multiplication, and thermal mitigation. These techniques are challenging as frequency and/or power is increased due to interconnect parasitics effects, especially in the millimeter wave (mmW) and terahertz (THz) regimes. Thus, it is desirable to have a transition frequency multiplier semiconductor device that has a structure with low inductive and capacitive parasitics. It is particularly desirable that the transition frequency multiplier semiconductor device be usable as a fundamental building block for extending the fT-breakdown product of short gate-length enhancement mode (E-mode) GaN transistor technology.

SUMMARY

A transition frequency multiplier semiconductor device having a first source region, a second source region, and a common drain region is disclosed. A first channel region is located between the first source region and the common drain region, and a second channel region is located between the second source region and the common drain region. A first gate region is located within the first channel region to control current flow between the first source region and the common drain region, while a second gate region is located within the second channel region to control current flow between the second source region and the common drain region. An inactive channel region is located between the first channel region and the second channel region such that the first channel region is electrically isolated from the second channel region.

In some exemplary embodiments, a conductive interconnect couples the first source region to the second gate region. In at least one embodiment, there is no conductive interconnect coupling between the first source region and the second gate region. Instead, there is an interconnect capacitor coupled between the first gate region and the second gate region. In yet another exemplary embodiment, the interconnect capacitor is coupled between the first source region and the second gate region.

Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

FIG. 1A is a schematic of a first embodiment of a transition frequency multiplier semiconductor device configured as a transition frequency doubler.

FIG. 1B is a cross sectional view of a device layout for the transition frequency multiplier semiconductor device, which in this first embodiment has a Darlington like configuration shown in FIG. 1A.

FIG. 2 is a graph of extrapolated cut-off frequency for an enhancement mode (E-mode) gallium nitride (GaN) high electron mobility transistor (HEMT) version of the transition frequency multiplier semiconductor device.

FIG. 3A is a schematic of a second embodiment of the transition frequency multiplier semiconductor device configured to provide a higher transition frequency than the first embodiment of FIGS. 1A and 1B.

FIG. 3B is a cross sectional view of a device layout for the transition frequency multiplier semiconductor device, which in the second embodiment has a Darlington like configuration shown in FIG. 3A.

FIG. 4A is a schematic of a third embodiment of the transition frequency multiplier semiconductor device of FIGS. 1A and 1B that further includes thin film resistors.

FIG. 4B is a cross sectional view of a device layout for the third embodiment of the transition frequency multiplier semiconductor device that includes the thin film resistors.

FIG. 5 is an exemplary structural diagram of a transition frequency multiplier array made up of a plurality of transition frequency multiplier semiconductor devices.

FIG. 6A is a cross sectional view of a device layout for a fourth embodiment of the transition frequency multiplier semiconductor device of FIGS. 1A and 1B that is a ‘stacked’ fT-multiplier.

FIG. 6B is a schematic of the fourth embodiment of the transition frequency multiplier semiconductor device configured to provide a higher effective source to drain breakdown voltage (BVds) than the previous embodiments.

FIG. 7A is a cross sectional view of a device layout for a fifth embodiment of the transition frequency multiplier semiconductor device of FIGS. 1A and 1B that further illustrates a slight modification to the stacked fT-multiplier of the fourth embodiment shown in FIGS. 6A and 6B.

FIG. 7B is a schematic diagram of the fifth embodiment of the transition frequency multiplier semiconductor device as structured in FIG. 7A.

FIG. 8A is a cross sectional view of a device layout for a sixth embodiment of the transition frequency multiplier semiconductor device of FIGS. 1A and 1B. In the sixth embodiment the first channel region has only the first gate region and the second channel region includes both the second gate region and the fourth gate region.

FIG. 8B is a schematic that symbolically illustrates the sixth embodiment of the transition frequency multiplier semiconductor device of FIGS. 1A and 1B that is depicted structurally in FIG. 8A.

FIG. 9 is a graph showing simulated results for a wideband amplifier implementation using a stacked version of the transition frequency multiplier semiconductor device in comparison with a conventional common-source transistor amplifier.

FIG. 10A is a schematic diagram of a triple Darlington type configuration with feedback that is a seventh embodiment of the transition frequency multiplier semiconductor device.

FIG. 10B is a schematic diagram of the triple Darlington type configuration with feedback and a first stacking transistor group that makes up an eighth embodiment of the transition frequency multiplier semiconductor device.

FIG. 10C is a schematic diagram of the triple Darlington type configuration with feedback and the first stacking transistor group along with a second stacking transistor group that makes up a ninth embodiment of the transition frequency multiplier semiconductor device.

FIG. 11A is a schematic diagram of a Darlington type configuration with feedback that makes up a tenth embodiment of the transition frequency multiplier semiconductor device.

FIG. 11B is a schematic diagram of the Darlington type configuration with feedback and a first stacking transistor pair that makes up an eleventh embodiment of the transition frequency multiplier semiconductor device.

FIG. 11C is a schematic diagram of the Darlington type configuration with feedback and a first stacking transistor pair along with a second stacking transistor pair that makes up a twelfth embodiment of the transition frequency multiplier semiconductor device.

FIG. 12 is a graph of 5 dB compressed output power over frequency a non-stacked Darlington operating at 3V, a stacked Darlington operating at 6V, and a Triple stacked Darlington operating at 9V.

FIG. 13 illustrates is a graph of third order intercept (IP3) linearity over frequency for a non-stacked Darlington operating at 3V, a stacked Darlington operating at 6V, and a Triple stacked Darlington operating at 9V.

FIG. 14A is a cross sectional view of a device layout for a thirteenth embodiment of the transition frequency multiplier semiconductor device that includes at least one additional gate region that extends across the first channel region.

FIG. 14B is a schematic that symbolically illustrates the thirteenth embodiment of the transition frequency multiplier semiconductor device as depicted structurally in FIG. 14A.

FIG. 15 is a schematic diagram of the triple Darlington type configuration with feedback and a first stacking transistor group that makes up a fourteenth embodiment of the transition frequency multiplier semiconductor device in which a source of a third transistor is coupled directly to RF ground.

FIG. 16A is a schematic of a fifteenth embodiment of the transition frequency multiplier semiconductor device that is configured to provide independent biasing of transistors integrated within the transition frequency multiplier semiconductor device.

FIG. 16B is a cross sectional view of a device layout for the transition frequency multiplier semiconductor device, which in this fifteenth embodiment has a configuration as shown in FIG. 16A.

FIG. 17 is an exemplary structural diagram of a transition frequency multiplier array made up of a plurality of transition frequency multiplier semiconductor devices that are depicted in FIG. 16B.

FIG. 18A is a schematic of a sixteenth embodiment of the transition frequency multiplier semiconductor device that is configured to provide independent biasing of transistors integrated within the transition frequency multiplier semiconductor device.

FIG. 18B is a cross sectional view of a device layout for the transition frequency multiplier semiconductor device, which in this sixteenth embodiment has a configuration as shown in FIG. 18A.

FIG. 19 is an exemplary structural diagram of a transition frequency multiplier array made up of a plurality of transition frequency multiplier semiconductor devices that are depicted in FIG. 18B.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood that when an element such as a layer, region, or substrate is referred to as being “over,” “on,” “in,” or extending “onto” another element, it can be directly over, directly on, directly in, or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over,” “directly on,” “directly in,” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

FIG. 1A is a schematic of a first embodiment of a transition frequency multiplier semiconductor device 10 configured as a transition frequency doubler. The transition frequency multiplier semiconductor device 10 is represented symbolically by a first transistor M1 and a second transistor M2 coupled in a Darlington like configuration. The first transistor M1 has a first gate region G1, a first drain region D1, and a first source region S1. The second transistor M2 has a second gate region G2, a second drain region D2, and a second source region S2. The first drain region D1 and the second drain region D2 form a common drain region 12 that is coupled to an output terminal 14. The first gate region G1 is coupled to an input terminal 16. The first source region S1 is coupled to the second gate region G2 by way of a conductive interconnect 18. A first resistor R1 couples the first source region S1 to an RF ground region 20, and a second resistor R2 couples the second source region S2 to the RF ground region 20. The first resistor R1 can be a current source bulk resistance that sets a bias point for the first transistor M1. The second resistor R2 can be a bulk resistance that provides feedback for setting RF and direct current (DC) characteristics for the transition frequency multiplier semiconductor device 10. The first resistor R1 can be replaced by a diode connected gated channel to provide current source biasing for the first transistor M1. In an exemplary embodiment, resistivities of the first resistor R1 and the second resistor R2 are provided by selective implantation damage resistivity determined by un-gated channel epitaxy resistivity.

FIG. 1B is a cross sectional view of a device layout for the transition frequency multiplier semiconductor device 10, which in this first embodiment has the Darlington like configuration shown in FIG. 1A. Fabrication of the transition frequency multiplier semiconductor device 10 involves reconfiguring a common-source multi-finger device structure by ion implantation damage or by a selective mesa etch to isolate the first source region S1 from the second source region S2, and to isolate the first gate region G1 from the second gate region G2. The common drain region 12 is not sub-divided and maintains a continuous stripe connection as typical for a single multi-finger device, which is true for all embodiments of this disclosure. Low inductive and low capacitive parasitics are obtained by using the continuous stripe connection to realize the common drain region 12.

Although the schematic of FIG. 1A symbolically depicts two transistors (i.e., the first transistor M1 and the second transistor M2), the transition frequency multiplier semiconductor device 10 is a compact composite device partially due to common drain region 12. In this exemplary case, the transition frequency multiplier semiconductor device 10 is the multi-fingered common source (CS) device that follows a D-G-S-G-D stripe formation typically found in a conventional multi-finger field effect transistor (FET) device. A first channel region 22 and a second channel region 24 are defined by implantation. The first gate region G1 and the second gate region G2 are formed by omitting gate metal formation in the middle of a first gate stripe that would typically be present if the first gate region G1 and the second gate region G2 were continuously coupled. The first channel region 22 and the second channel region 24 are separated by an inactive channel region 26 that can be formed by an isolated damage implant or alternatively by a mesa etch isolation. The inactive channel region 26 is depicted within a dashed outline that defines the first channel region 22 from the second channel region 24. The first source region S1 and the second source region S2 are also separated by the inactive channel region 26. Note that the first gate region G1, the first channel region 22, and the first source region S1 each have a first width WG1. The second gate region G2, the second channel region 24, and the second source region S2 each have a second width WG2. In this first embodiment, the first width WG1 and the second width WG2 are substantially equal.

In this exemplary embodiment, the inactive channel region 26 can be continuous with an un-gated channel region 28 that separates the first source region S1 and the second source region S2 from the RF ground region 20. Selective implantation can extend from the un-gated channel region 28 to along edges of the transition frequency multiplier semiconductor device 10. Similar to the fabrication of the inactive channel region 26, the un-gated channel region 28 can also be formed by a selective implant such as ion implantation damage or alternatively by a mesa etch isolation. The first source S1 is electrically coupled to the second gate region G2 by the conductive interconnect 18. In this exemplary case, the RF ground region 20 includes a ground slot via 30.

In at least one embodiment, the first resistor R1 and the second resistor R2 are both compact low parasitic bulk resistors that are located within the un-gated channel region 28. Resistance values of the first resistor R1 and the second resistor R2 are defined by selective implantation. In some exemplary embodiments, resistivities of the first resistor R1 and the second resistor R2 are provided by selective implantation damage resistivity determined by un-gated channel epitaxy resistivity. The first resistor R1 and the second resistor R2 in at least one embodiment terminate onto a subsequent drain/source region that comprises the RF ground region 20 and the ground slot via 30. The compact composite device structure shown in FIG. 1B provides an area efficient design that is conducive of high frequency performance that is scalable in size to meet given power requirements.

FIG. 2 is a graph of extrapolated cut-off frequency for an enhancement mode (E-mode) gallium nitride (GaN) high electron mobility transistor (HEMT) version of the transition frequency multiplier semiconductor device 10. Based on a typical E-mode GaN technology with a measured transition frequency (fT) of approximately 289 GHz and a drain to gate breakdown voltage (BVdg) of 11V, a simulated fT of the embodiment of FIGS. 1A and 1B based on measured transistor S-parameters is 496 GHz (˜500 GHz). In this case, the fT is increased by a factor of 1.7 times over a typical common-source configuration having an fT of 289 GHz. The factor of 1.7 is a practical limit due to non-idealities in the transition frequency multiplier semiconductor device 10. Some of the non-idealities are associated with the first resistor R1.

FIG. 3A is a schematic of a second embodiment of the transition frequency multiplier semiconductor device 10 that is configured to provide an fT that is higher than the first embodiment of FIGS. 1A and 1B. The second embodiment is similar to the first embodiment, except that the width WG2 of the second gate region G2, the second channel region 24, and the second source region S2, is increased substantially with respect to the first width WG1 of the first channel region 22, the first gate region G1, and the first source region S1. In the exemplary case of FIG. 3B, the second width WG2 is around twice that of the first width WG1. A simulated performance of the case wherein the second width WG2 is two times the first width WG1 predicts an fT of ˜674 GHz resulting in a 2.3 times increase in effective fT for a same drain to source voltage (Vds) operation with respect to a common-source device, which has an fT of ˜289 GHz. This is an additional 35.6% improvement in fT compared to the fT-doubler case of embodiment 1 where WG2 is equal to WG1.

It is to be understood that the first and second embodiments of the transition frequency multiplier semiconductor device 10 is extendable to a triple Darlington-like topology to increase fT even further. By adding yet a third transistor and a third resistor at the input of the schematics of either FIG. 1A or FIG. 1B, a higher fT of 824 GHz is predicted as illustrated in FIG. 2. Combined with further improvements in the base technology, THz cut-off frequencies are feasible.

Other embodiments of this disclosure increase the operating voltage of the transition frequency multiplier semiconductor device 10 by adding stacked or multiple gates within a long channel region termed “stacked fT-multiplier” in order to further increase the fT-breakdown voltage product (Johnson Figure of Merit). Stacked fT-multiplier embodiments are described in later sections of this disclosure. With the stacked fT-multiplier embodiments, a Johnson Figure of Merit as high as 15 THz-V, or 3 times that predicted by GaN HEMTs, may be feasible based on simulations.

FIG. 4A is a schematic of a third embodiment of the transition frequency multiplier semiconductor device 10 in which the first resistor R1 and the second resistor R2 are thin film resistors instead of bulk resistors. FIG. 4B is a cross sectional view of a device layout for a third embodiment of the transition frequency multiplier semiconductor device 10 that includes the thin film resistors. In this case the un-gated channel region 28 extends uninterrupted above the RF ground region 20. Thin film resistors are typically more accurately processed. Thus, some better control over bias operating points can be achieved. However, it is to be understood that combinations of thin film resistor types and bulk resistor types can be used to maximize total performance of the transition frequency multiplier semiconductor device 10.

FIG. 5 is an exemplary structural diagram of a transition frequency multiplier array 32 made up of a plurality of transition frequency multiplier semiconductor devices 10-1 through 10-N. This embodiment is very similar to a single multi-finger device cell where alternating stripes may include S-G-D regions with integrated slot vias on select source or drain stripes to provide low source inductance and high frequency performance. This particular embodiment also emphasizes the scaling benefits of a striped composite device structure that resembles a single multi-finger field effect transistor (FET) transistor device.

The transition frequency multiplier array 32 that is an NX array is made up of N number of transition frequency multiplier semiconductor devices 10-N that are coupled together, wherein N is a finite integer. The transition frequency multiplier semiconductor device 10-N has a first gate region G1-N, a first drain region D1-N, and a first source region S1-N. The transition frequency multiplier semiconductor device 10-N also includes a second gate region G2-N, a second drain region D2-N, and a second source region S2-N. The first drain region D1-N and the second drain region D2-N form a common drain region 12-N that is coupled to an output terminal 14-N. The first gate region G1-N is coupled to an input terminal 16-N. The first source region S1-N is coupled to the second gate region G2-N by way of a conductive interconnect 18-N. A first resistor R1-N couples the first source region S1-N to an RF ground region 20-N, and a second resistor R2-N couples the second source region S2-N to the RF ground region 20-N. The first resistor R1-N can be a current source bulk resistance and the second resistor R2-N can be a bulk resistance that provides feedback for setting RF and direct current (DC) characteristics for the transition frequency multiplier semiconductor device 10-N. The first resistor R1-N can be replaced by a diode connected gated channel to provide the current source biasing.

Fabrication of the transition frequency multiplier semiconductor device 10-N involves reconfiguring a common-source multi-finger device structure by ion implantation damage or by a selective mesa etch to isolate the first source region S1-N from the second source region S2-N, and to isolate the first gate region G1-N from the second gate region G2-N. The common drain region 12-N is not sub-divided and maintains a continuous stripe connection as typical for a single multi-finger device, which is true for all embodiments of this disclosure. Low inductive and low capacitive parasitics are obtained by using the continuous stripe connection to realize the common drain region 12-N.

The transition frequency multiplier semiconductor device 10-N is a compact composite device partially due to common drain region 12-N. In this exemplary case, the transition frequency multiplier semiconductor device 10-N is the multi-fingered common source (CS) device that follows a D-G-S-G-D stripe formation typically found in a conventional multi-finger FET device. A first channel region 22-N and a second channel region 24-N are defined by selective implantation. The first gate region G1-N and the second gate region G2-N are formed by omitting gate metal formation in the middle of a first gate stripe that would typically be present if the first gate region G1-N and the second gate region G2-N were continuously coupled. The first channel region 22-N and the second channel region 24-N are separated by an inactive channel region 26-N that can be formed by an isolated damage implant or alternatively by a mesa etch isolation. The inactive channel region 26-N is depicted within a dashed outline that defines boundaries between the first channel region 22-N and the second channel region 24-N. The first source region S1-N and the second source region S2-N are also separated by the inactive channel region 26-N.

In this exemplary embodiment, the inactive channel region 26-N can be continuous with an un-gated channel region 28-N that separates the first source region S1-N and the second source region S2-N from the RF ground region 20-N. Selective implantation can extend from the un-gated channel region 28-N to along edges of the transition frequency multiplier semiconductor device 10-N. Similar to the fabrication of the inactive channel region 26, the un-gated channel region 28-N can also be formed by a selective implant such as ion implantation damage or alternatively by a mesa etch isolation. The first source S1-N is electrically coupled to the second gate region G2-N by the conductive interconnect 18-N. In this exemplary case, the RF ground region 20-N includes a ground slot via 30-N.

In at least one embodiment, the first resistor R1-N and the second resistor R2-N are both compact low parasitic bulk resistors that are located in an un-gated channel region 28-N. Resistance values of the first resistor R1-N and the second resistor R2-N are defined by selective implantation. The first resistor R1-N and the second resistor R2-N in at least one embodiment terminate onto a subsequent drain/source region that comprises the RF ground region 20-N and the ground slot via 30-N.

A 2× array version of the transition frequency multiplier array 32 comprises only the transition frequency multiplier semiconductor device 10-1 coupled to the transition frequency multiplier semiconductor device 10-2. Notice that the transition frequency multiplier semiconductor device 10-1 and the transition frequency multiplier semiconductor device 10-2 share RF ground region 20-1 and ground slot via 30-1. A 3× array version of the transition frequency multiplier array 32 comprises the transition frequency multiplier semiconductor device 10-2 coupled in between the transition frequency multiplier semiconductor device 10-1 and the transition frequency multiplier semiconductor device 10-N, where N in this particular case is equal to 3. In this particular case, where N equals 3, the transition frequency multiplier semiconductor device 10-N is inverted such that the common drain region 12-N and the common drain region 12-2 are one and the same. Other embodiments of the transition frequency multiplier array 32 include but are not limited to a 4× array version and an 8× array version. An even higher fT-breakdown product or Johnson Figure of Merit (JFoM) is achieved in other embodiments by effectively stacking gated channels in the fT-multiplier, and thereby increasing the effective breakdown and operating voltage.

FIG. 6A is a cross sectional view of a device layout for a fourth embodiment of the transition frequency multiplier semiconductor device 10 that is a ‘stacked’ fT-multiplier. This fourth embodiment is similar to the second embodiment of FIG. 3, except that the first channel region 22 and the second channel region 24 are increased in length, with increased source to drain channel spacing to provide higher BVdg. In addition to a first gate region G1A and a second gate region G2A, a single metal gate stripe makes up a third gate region G1B and a fourth gate region G2B. The addition of the third gate region G1B and the fourth gate region G2B converts the first channel region 22 and the second channel region 24 into stacked channel regions. As a result, this fourth embodiment of the transition frequency multiplier semiconductor device 10 provides both increased breakdown voltage and increased transition frequency that combine to increase the JFoM.

FIG. 6B is a schematic of a fourth embodiment of the transition frequency multiplier semiconductor device 10 configured to provide a higher effective BVds than the previous embodiments. In this particular case, an active channel made up of the first channel region 22 and the second channel region 24 are represented as a third transistor M1B and a fourth transistor M2B that form two separate cascoded stacked devices in conjunction with the first transistor M1A and the second transistor M2A. The third gate region G1B of the third transistor M1B and the fourth gate region G2B of the fourth transistor M2B are coupled together in this exemplary embodiment. Note that the first transistor M1A and the third transistor M1B are not individual stacked transistor devices in the layout of FIG. 6A, but are instead similar to a typical dual gated channel structure.

The third gate region G1B and the fourth gate region G2B are controlled together by a control signal applied to a control terminal ZV1. However, the first channel region 22 and the second channel region 24 remain isolated by the inactive channel region 26 similar to the previous embodiments.

FIG. 7A is a cross sectional view of a device layout for a fifth embodiment of the transition frequency multiplier semiconductor device 10 that illustrates a slight modification to the stacked fT-multiplier of the fourth embodiment. FIG. 7B is a schematic diagram of the fifth embodiment of the transition frequency multiplier semiconductor device as structured in FIG. 7A. In this case, the third gate region G1B and the fourth gate region G2B are separated to provide individual and separate gate control of the third transistor M1B and the fourth transistor M2B as schematically represented in FIG. 7B. The separation of the third gate region G1B and the fourth gate region G2B allows more design flexibility in providing desired biases and gate termination impedances. For example, having a different impedance on a first control terminal ZV1 than on a second control terminal ZV2 can provide more linear voltage swing for the first transistor M1A, which is raised by one gate to source voltage level of the second transistor M2A above ground potential applied to the RF ground region 20.

FIG. 8A is a cross sectional view of a device layout for a sixth embodiment of the transition frequency multiplier semiconductor device 10 in which the first channel region 22 has only the first gate region G1A and the second channel region 24 includes both the second gate region G2A and the fourth gate region G2B. FIG. 8B is a schematic that symbolically illustrates the sixth embodiment of the transition frequency multiplier semiconductor device 10 that is depicted structurally in FIG. 8A. The second channel region 24 has a longer source to drain length that increases operating voltage and accommodates the stacked arrangement of the second gate region G2A and the fourth gate region G2B. As a result of the stacked structure of the second channel region 24, impedance and bias presented to the fourth gate region G2B is adjustable for a desired amplifier performance.

FIG. 9 is a graph showing simulated results for a wideband amplifier implementation using a stacked version of the transition frequency multiplier semiconductor device 10 in comparison with a conventional common-source transistor amplifier. Simulations of the transition frequency multiplier semiconductor device 10 and the conventional common-source transistor amplifier were both conducted based upon 11V BVdg 289 GHz E-GaN HEMT technology. The plots in the graph of FIG. 9 illustrate that a stacked version of the transition frequency multiplier semiconductor device 10 achieves much wider gain bandwidth as well as matched output impedance as a result of employing both the fT-multiplier and stacked structures. Scattering parameters S11, S21, and S22 are plotted for both the common-source device represented in dashed line and the stacked fT multiplier device performance of the transition frequency multiplier semiconductor device 10 are represented in solid line.

FIG. 10A is a schematic diagram of a triple Darlington type configuration 34 with feedback that makes up a seventh embodiment of the transition frequency multiplier semiconductor device 10. The feedback is provided by coupling a feedback resistor RFB1 from the output to the input. The triple Darlington type configuration 34 adds a third Darlington transistor M3 with a source resistor R3 coupled between a third source region S3 and RF ground region 20. A third gate region G3 of the third transistor M3 is coupled to the second source region S2 of the second transistor M2. A third drain region D3 is coupled to the common drain region 12. This particular embodiment is referred herein as a non-stacked triple Darlington.

FIG. 10B is a schematic diagram of the triple Darlington type configuration 34 with feedback and a first stacking transistor group 36 that makes up an eighth embodiment of the transition frequency multiplier semiconductor device 10. This particular embodiment is referred to herein as a stacked Darlington.

FIG. 10C is a schematic diagram of the triple Darlington type configuration 34 with feedback and the first stacking transistor group 36 along with a second stacking transistor group 38 that makes up a ninth embodiment of the transition frequency multiplier semiconductor device 10. This particular embodiment is referred to herein as a triple stacked triple Darlington.

FIG. 11A is a schematic diagram of a Darlington type configuration 40 with feedback that makes up a tenth embodiment of the transition frequency multiplier semiconductor device 10. The feedback is provided by coupling the feedback resistor RFB1 from the output to the input. This particular embodiment is referred to herein as a non-stacked Darlington.

FIG. 11B is a schematic diagram of the Darlington type configuration 40 with feedback and a first stacking transistor pair 42 that makes up an eleventh embodiment of the transition frequency multiplier semiconductor device 10. This particular embodiment is referred to herein as a stacked Darlington.

FIG. 11C is a schematic diagram of the Darlington type configuration 40 with feedback and the first stacking transistor pair 42 along with a second stacking transistor pair 44 that makes up a twelfth embodiment of the transition frequency multiplier semiconductor device 10. This particular embodiment is referred to herein as a triple stacked triple Darlington.

FIG. 12 is a graph of 5 dB compressed output power over frequency a non-stacked Darlington operating at 3V (FIG. 11A), a stacked Darlington operating at 6V (FIG. 11B), and a Triple stacked Darlington (FIG. 11C) operating at 9V. The improvement in output capability by stacking devices and operating at higher Vdd voltage is illustrated FIG. 12.

FIG. 13 illustrates is a graph of third order intercept (IP3) linearity over frequency for a non-stacked Darlington operating at 3V (FIG. 11A), a stacked Darlington operating at 6V (FIG. 11B), and a Triple stacked Darlington (FIG. 11C) operating at 9V. Relatively dramatic improvements in amplifier linearity by stacking devices and operating at higher Vdd voltage are illustrated in FIG. 13.

FIG. 14A is a cross sectional view of a device layout for a thirteenth embodiment of the transition frequency multiplier semiconductor device 10 in which the second channel region 24 has only the second gate region G2A and the first channel region 22 includes both the first gate region G1A and the third gate region G1B that extends across the first channel region 22. FIG. 14B is a schematic that symbolically illustrates the thirteenth embodiment of the transition frequency multiplier semiconductor device 10 that is depicted structurally in FIG. 14A. As a result of the stacked structure of the first channel region 22, impedance and bias presented to the third gate region G1B is adjustable for a desired amplifier performance. For example, a tuning network can be coupled to the control terminal ZV1. Tuning control of the gate region G1B can provide linearization by cancelling harmonics produced by the first transistor M1A and the second transistor M2A, as an example.

FIG. 15 is a schematic diagram of the triple Darlington type configuration 34 with feedback and a first stacking transistor group 36 that makes up a fourteenth embodiment of the transition frequency multiplier semiconductor device 10 in which the third source S3 is coupled directly to RF ground. This exemplary configuration is particularly useful in instances wherein no source feedback resistor is needed for the last transistor of an output stage. FIG. 15 also depicts an RF signal source RF1 coupled to the first gate region G1 of the first transistor M1. In one exemplary embodiment, transition frequency multiplier semiconductor device 10 amplifies an RF signal provided by the RF signal source RF1, wherein the RF signal has a frequency between 30 GHz and 110 GHz. In another exemplary embodiment, the transition frequency multiplier semiconductor device 10 amplifies an RF signal provided by the RF signal source RF1, wherein the RF signal has a frequency between 110 GHz and 1000 GHz.

FIG. 16A is a schematic of a fifteenth embodiment of the transition frequency multiplier semiconductor device 10 that is configured to provide independent electronic biasing of both the first transistor M1 and the second transistor M2. FIG. 16B is a cross sectional view of a device layout for the fifteenth embodiment shown schematically in FIG. 16A. In this fifteenth embodiment, as depicted in FIG. 16A and FIG. 16B, the conductive interconnect 18 of the previous embodiments is removed such that there is no conductive path between the first source region S1 and the second gate region G2. Instead, an interconnect capacitor C1 is coupled between the first gate region G1 of the first transistor M1 and the second gate region G2 of the second transistor M2. The interconnect capacitor C1 depicted symbolically in FIG. 16B can be a metal-insulator-metal capacitor fabricated from metal layers and dielectric of the inactive channel region 26.

A benefit of this fifteenth embodiment is that the independent bias configuration provides independent asymmetrical biasing of the first transistor M1 and the second transistor M2 that in this exemplary case yields two conductance functions in parallel. The conductance functions then allow linearization of the transition frequency multiplier semiconductor device 10 by providing a first tunable bias point for the first transistor M1 that is independently tunable from a second tunable bias point for the second transistor M2.

FIG. 17 is an exemplary structural diagram of a transition frequency multiplier array 46 made up of a plurality of transition frequency multiplier semiconductor devices 10-1 through 10-N that are the fifteenth embodiment depicted in FIG. 16B. In this embodiment, each of the transition frequency multiplier semiconductor devices 10 has an interconnect capacitor depicted symbolically in FIG. 17 as C1, and C2 through CN.

FIG. 18A is a schematic of a sixteenth embodiment of the transition frequency multiplier semiconductor device 10 that is configured to provide independent electronic biasing of both the first transistor M1 and the second transistor M2. FIG. 18B is a cross sectional view of a device layout for the fifteenth embodiment shown schematically in FIG. 18A. In this sixteenth embodiment, as depicted in FIG. 18A and FIG. 18B, the conductive interconnect 18 is removed such that there is no conductive path between the first source region S1 and the second gate region G2. Instead, an interconnect capacitor C1 is coupled between the first source region S1 of the first transistor M1 and the second gate region G2 of the second transistor M2. The interconnect capacitor C1 depicted symbolically in FIG. 18B can be a metal-insulator-metal capacitor fabricated from metal layers and dielectric of the inactive channel region 26.

A benefit of this sixteenth embodiment is that the independent bias configuration provides independent asymmetrical biasing of the first transistor M1 and the second transistor M2 that in this exemplary case yields two conductance functions in parallel, while also enhancing transition frequency performance. The conductance functions then allow linearization of the transition frequency multiplier semiconductor device 10 by providing a first tunable bias point for the first transistor M1 that is independently tunable from a second tunable bias point for the second transistor M2.

FIG. 19 is an exemplary structural diagram of a transition frequency multiplier array 48 made up of a plurality of transition frequency multiplier semiconductor devices 10-1 through 10-N that are the fifteenth embodiment depicted in FIG. 18B. In this embodiment, each of the transition frequency multiplier semiconductor devices 10 has an interconnect capacitor depicted symbolically in FIG. 17 as C1 and C2 through CN.

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow. 

What is claimed is:
 1. A transition frequency multiplier semiconductor device comprising: a first source region; a second source region; a common drain region; a first channel region located between the first source region and the common drain region; a second channel region located between the second source region and the common drain region; a first gate region located within the first channel region to control current flow between the first source region and the common drain region; a second gate region located within the second channel region to control current flow between the second source region and the common drain region; and an inactive channel region located between the first channel region and the second channel region such that the first channel region is electrically isolated from the second channel region.
 2. The transition frequency multiplier semiconductor device of claim 1 further including an interconnect capacitor coupled between the first gate region and the second gate region.
 3. The transition frequency multiplier semiconductor device of claim 1 further including an interconnect capacitor coupled between the first source region and the second gate region.
 4. The transition frequency multiplier semiconductor device of claim 3 wherein the interconnect capacitor is a metal-insulator-metal capacitor.
 5. The transition frequency multiplier semiconductor device of claim 1 further including a conductive interconnect coupled between the first source region and the second gate region.
 6. The transition frequency multiplier semiconductor device of claim 5 wherein the conductive interconnect has a length between the first source region and the second source region that is no greater than 5% of a wavelength of a radio frequency signal applied to the first gate region.
 7. The transition frequency multiplier semiconductor device of claim 6 wherein the radio frequency signal is between 30 GHz and 110 GHz.
 8. The transition frequency multiplier semiconductor device of claim 6 wherein the radio frequency signal is between 110 GHz and 1000 GHz.
 9. The transition frequency multiplier semiconductor device of claim 1 further including at least one additional gate region that extends across the first channel region.
 10. The transition frequency multiplier semiconductor device of claim 1 wherein the inactive channel region is an isolated damage implant.
 11. The transition frequency multiplier semiconductor device of claim 1 further comprising: an RF ground region; and an un-gated channel region between the first source region, the second source region, and the RF ground region.
 12. The transition frequency multiplier semiconductor device of claim 11 further including a first resistor coupled between the first source region and the RF ground region and a second resistor coupled between the second source region and the RF ground region.
 13. The transition frequency multiplier semiconductor device of claim 12 wherein resistivities of the first resistor and the second resistor are provided by selective implantation damage resistivity determined by un-gated channel epitaxy resistivity.
 14. The transition frequency multiplier semiconductor device of claim 12 further including a third source region coupled directly to the RF ground region and a third gate region coupled to the second source region.
 15. A transition frequency multiplier semiconductor device comprising: a first source region; a second source region; a common drain region; a first channel region located between the first source region and the common drain region; a second channel region located between the second source region and the common drain region; a first gate region located within the first channel region to control current flow between the first source region and the common drain region; a second gate region located within the second channel region to control current flow between the second source region and the common drain region; at least one additional gate region that extends across the first channel region and/or at least one additional gate region that extends across the second channel region; and an inactive channel region located between the first channel region and the second channel region such that the first channel region is electrically isolated from the second channel region.
 16. The transition frequency multiplier semiconductor device of claim 15 further including an interconnect capacitor coupled between the first gate region and the second gate region.
 17. The transition frequency multiplier semiconductor device of claim 15 further including an interconnect capacitor coupled between the first source region and the second gate region.
 18. The transition frequency multiplier semiconductor device of claim 17 wherein the interconnect capacitor is a metal-insulator-metal capacitor.
 19. The transition frequency multiplier semiconductor device of claim 15 further including a conductive interconnect coupled between the first source region and the second gate region.
 20. A transition frequency multiplier array comprising: a plurality of transition frequency multiplier semiconductor devices that each comprise: a first source region; a second source region; a common drain region; a first channel region located between the first source region and the common drain region; a second channel region located between the second source region and the common drain region; a first gate region located within the first channel region to control current flow between the first source region and the common drain region; a second gate region located within the second channel region to control current flow between the second source region and the common drain region; at least one additional gate region that extends across the first channel region and/or at least one additional gate region that extends across the second channel region; an inactive channel region located between the first channel region and the second channel region such that the first channel region is electrically isolated from the second channel region; and an RF ground region, wherein adjacent ones of the plurality of transition frequency multiplier semiconductor devices are coupled together by adjacent ones of the RF ground region.
 21. The transition frequency multiplier array of claim 20 wherein each of the plurality of transition frequency multiplier semiconductor devices further comprises an interconnect capacitor coupled between the first gate region and the second gate region.
 22. The transition frequency multiplier array of claim 20 wherein each of the plurality of transition frequency multiplier semiconductor devices further comprises an interconnect capacitor coupled between the first source region and the second gate region.
 23. The transition frequency multiplier array of claim 22 the interconnect capacitor is a metal-insulator-metal capacitor.
 24. The transition frequency multiplier array of claim 20 wherein each of the plurality of transition frequency multiplier semiconductor devices further comprise an un-gated channel region between the first source region, the second source region, and the RF ground region. 